Acceleration: The process of moving faster or happening more quickly. As the ping-pong ball moves down the zip line, it accelerates, or goes faster.
Force: A push or pull on an object. Gravity is a force that pulls us toward the center of the Earth.
Friction: The force that slows objects down when they are rubbing against each other. Some things make lots of friction, like brakes on a tire, and some make very little friction, like skates on ice.
Gravity: A force of attraction that occurs between all objects. We experience it as the constant force that pulls objects toward the center of the Earth.
Mass: The amount of matter in an object. The more the mass, the heavier the object.
Slope: The direction and steepness of a line. Slope is measured by the vertical drop divided by the horizontal distance covered by the line.
Speed: The distance traveled over a period of time. If something is accelerating, it is moving at a faster speed.
Weight: The force of gravity on an object. The more something weighs, the stronger the force of gravity.